When scientists talk about the cryosphere, they mean the places on Earth where water is in its solid form, frozen into ice or snow. Read more ...

Service Interruption

On Monday, 11 July from 3:00 p.m. through Wednesday, 13 July until 5:00 p.m. (USA Mountain Time), NSIDC data distribution, services, and Web site will be unavailable to accommodate a major upgrade to our data center. We apologize for any inconvenience this may cause you.
Need to talk to us? You can always contact our friendly User Services Office at nsidc@nsidc.org or + 1 303.492.6199.

Issue 10, Summer 1994

PRODUCTS AND SERVICES

Eight CD-ROM volumes of DMSP F-11 SSM/I Brightness Temperature Grids for the Polar Regions are now available from NSIDC! The eight F-11 SSM/I CD- ROMs, derived from Remote Sensing Systems Antenna Temperature tapes, represent all data available to NSIDC at press time. These eight volumes include temporal coverage from 3 December 1993 through 28 February 1994.

Changing over to an SGI Challenge L server has allowed NSIDC to process three months of SSM/I data in three days. Quality assurance checks take two to three more days, mastering and duplication requires approximately 10 days.

If you have not responded to our questionnaire regarding your interest in this SSM/I data product, you will not receive CD-ROMs from this DMSP F11 SSM/I series. Please return the questionnaire as soon as possible so that we may include you on our DMSP F11 SSM/I standing order list. If you did not receive a questionnaire, or have misplaced it, contact NSIDC User Services to receive a copy of the questionnaire by mail, fax, or e-mail.

Only two F-11 data recorders remain functional. The following explanation summarizes an e-mail message from Pam Taylor (NOAA/NESDIS) 1 February 1994 to distribution:

As of 00Z 1 February 1994 the DMSP F-11 spacecraft lost a second of its four recorders. This recorder, in tended to supply global mission sensor data (SSM/T-1, SSM/T-2 and SSM/I), grew increasingly noisy and became unintelligible Friday, 28 January 1994. One of the available recorders is dedicated to OLS fine (high resolution) data. The other recorder is dedicated to the OLS smooth (low resolution) data and the remaining sensors. Since the recorders cannot simultaneously record and download, four- to five-minute gaps have resulted near the DMSP readout sites (Alaska, New Hampshire, Washington, Hawaii and Greenland) for all mission data including the SSM/T, SSM/I and SSM/T-2 data.

The gaps will be seen in data beginning with 1 February 1994, on the CD-ROMs titled DMSP F-11 SSM/I Brightness Temperature Grids, Polar Regions, Vol. 9. Most of the data gaps are occurring in the northern US and southern Canada, with a few lapses in Greenland. Since all DMSP readout sites are in the Northern Hemisphere no gaps should occur in data for the Southern Hemisphere.

The monthly averaged sea ice data are in HDF (Hierarchical Data Format). Software to read and manipulate HDF data files as well as help in using the software is available from The HDF Group. IDL and other commercial and shareware packages can also be used to read and manipulate HDF files.

Please register with NSIDC User Services if you wish to be notified of updates and/or corrections to these monthly sea ice products.

We need to know that you are a user, so that we will be able to contact you in the event of errors or changes to the product.

NSIDC is now the official archive and distribution center for the Nimbus-7 SMMR-Derived Global Snow Cover and Snow Depth Grids, 1978-1987, formerly available from NASA's NSSDC and PLDS at Goddard Space Flight Center. These data are available on 8 mm tape, 9-track tape (6250 bpi), or 4 mm DAT tape, as well as via anonymous ftp.

NSIDC is developing a global snow cover product using SSM/I (1987 to present), that will be distributed in the Equal Area SSM/I Earth Grid (EASE-Grid). Watch these pages for news of the EASE-Grid snow cover product, a part of the EOSDIS Pathfinder effort.

During the first week of September, NSIDC mailed a new version of the documentation for the Comiso "boot strap" algorithm for calculating SSM/I ice concentrations to all holders of the DMSP SSM/I F8 Brightness Temperature and Ice Concentration Grids for the Polar Regions CD-ROMs. The text has been updated, and Table 1, "Slopes and Offsets Used by the Bootstrap Algorithm," has corrections both to the format of the table and to the slope and offset values in columns 2 and 3. We apologize for any inconvenience caused by the original version mailed during February 1994. Please discard the earlier version.

The NASATEAM algorithm text (D. Cavalieri, January 1994) is also provided in the September mailing, although no changes have been made in the Cavalieri text.

Within the next several weeks, we will be completing a major revision of the User's Guide for the DMSP F8 SSM/I CD-ROMs. This revision will incorporate the Comiso "bootstrap" algorithm text and the Cavalieri text. Subscribers to the DMSP F8 SSM/I CD-ROMs will automatically receive the new text of the User's Guide. The DMSP F8 SSM/I products cover 9 July 1987 to 31 December 1991.

If you have any questions regarding current or future versions of the DMSP F8 SSM/I documentation or data, or if by 30 September you have not received the new documentation for the Comiso "bootstrap" sea ice algorithm, please contact NSIDC User Services.

DMSP Operational Linescan System(OLS) visible and thermal infrared data from the NOAA/National Geophysical Data Center (NGDC) digital archive are now available from NSIDC. The data holdings available at this time are the OLS smooth resolution imagery (2.7 km) recorded after March 1, 1994. (Data recorded between March 1, 1993 and March 1, 1994 form the backlog of data yet to be processed at NGDC.) NSIDC is providing DMSP user services for the cryospheric user community. In the next few months this will include user services for the SSM/I passive microwave imager, SSM/T microwave temperature sounder, and SSM/T-2 microwave water vapor profiler.

Data distribution is primarily in digital form on 8 mm 2.5 or 5.0 Gbyte Exabyte tape or hard-copy prints and transparencies. A pricing schedule has been established by NOAA/NGDC. Charges for OLS data are $8 per orbit, plus $19 for the cost of the tape. Hard-copy images cost $23 each for prints and transparencies and $22 each for slides. TIF and GIF files are also available at $16 each. An $11 shipping charge applies to all orders. NOAA requires prepayment on all orders.

An Atlas E rocket launched the new Defense Meteorological Satellite Program spacecraft into a polar orbit on August 29. The satellite will undergo several weeks of tests before it begins providing weather data to military and civilian users. More details will follow in the next issue of NSIDC Notes.

ON GOING RESEARCH ACTIVITIES

NSIDC has compared a six-month time series of sea ice concentrations derived from two different gridding schemes. The Polar Stereographic sea ice concentrations (produced on CD-ROM by NSIDC) were compared with sea ice concentrations derived from EASE-Grid processing.

The polar stereographic binning method is a "drop-in the-bucket" averaging of all brightness temperatures falling into a grid cell for a given day. The EASE-Grid method utilizes coefficients derived from the antenna pattern to artificially increase swath sampling density. Brightness temperatures are assigned to grid cells by selecting the value of the nearest neighbor in the over-sampled array. Two images are produced per day (one from the ascending passes and one from the descending). Both methods start from swath data produced by Remote Sensing Systems.

The EASE-Grid data have advantages of increased temporal sampling and no data averaging. EASE-Grid was developed by NSIDC in collaboration with the SSM/I Products Working Team as a structure for Earth-gridded SSM/I data which provide global coverage. From the brightness temperatures, sea ice concentrations are calculated using the NASA Team algorithm.

For the time series analyzed, ascending and descending images of the EASE-Grid were averaged and re-sampled to a polar stereographic projection. A statistical analysis on the two data sets was then performed.

Figure 1 shows the mean absolute difference between sea ice concentration for the time series. The difference is small in the winter months; however, as melt occurs, the difference increases. The observed differences between the data sets as a whole are within the precision of the sea ice algorithm.

Figure 1. This shows the man absolute difference between sea ice concentration for the time series. The difference is small in the winter months; however, as melt occurs, the difference increases. The observed differences between the data sets as a whole are within the precision of the sea ice algorithm.

Examination of the distribution of differences between the data sets revealed the largest differences at the ice margin where variability in concentration is greatest on both temporal and spatial scales. To further investigate the ice margin, NSIDC has examined nine sub-regions of 3 x 3 pixels (75 km x 75 km). Again, differences were small in summer months and increased with melt. This trend was most apparent for static areas of ice concentration. More dynamic areas, the Sea of Okhotsk and the ice margin off the east coast of Greenland, showed greater variability throughout the time series. Again this is expected for areas where sea ice concentration is changing quickly over space and time. Comparisons were also made with ascending and descending sea ice concentrations alone in order to investigate the effects of the increased temporal sampling. Only one sub-region showed a consistent behavior/bias between the ascending and descending data sets, the area off the east coast of Greenland. NSIDC is continuing examination of this point.

ARCTIC SYSTEM SCIENCE (ARCSS)

From 11-14 September, the ARCSS/Greenland Ice Sheet Program2 investigators met at Algonkian Regional Park, Sterling, VA, to discuss their current and planned analyses of the GISP2 data, and to develop a publication plan for the Greenland ice sheet core data. Claire Hanson, NSIDC's ARCSS Data Project Manager, and Matthew Cross, NSIDC's ARCSS Data Coordinator, attended the meeting to present NSIDC's ideas for GISP2 data archiving and distribution, and to forge a stronger working relationship with the GISP2 investigators.

At the workshop, Claire and Matt presented NSIDC's plan to begin releasing data in cases where investigators have published results and have agreed to such a release. This is the first step leading to the eventual publication of a GISP2 compendium volume (jointly with GRIP, the European Greenland Icesheet Program), which would include a CD-ROM of GISP and GRIP data sets. If the process of releasing and documenting data begins now, there should be a significant body of data ready for the compendium in the scheduled 1995-96 time frame.

The archival and negotiated distribution of GISP2 data at NSIDC is being closely coordinated with the NOAA/National Geophysical Data Center's Paleoclimate Group, who have an ftp server in place for access to all types of paleoclimate data, including some GRIP data sets. NSIDC also provides data via ftp on request, but since the NSIDC computing environment is at this time driven primarily by the NASA/EOSDIS effort, it is not possible to implement a completely on-line ftp data server for the GISP2 and other ARCSS data. Any data held by NSIDC as part of the GISP2 and other ARCSS components will be staged for ftp pickup on request. Please contact NSIDC User Services for information on current availability of GISP2 or GRIP data.

Data from the Northeast Water Polynya (NEW) Project 1992 field season are now being archived at NSIDC as part of the ARCSS Data Coordination Center project. After the 1993 field season data are transferred (target date is late fall 1994), a set of "one-off" laser discs will be cut for the NEW investigators, to give them a way to access the entire NEW database in one convenient package. Their "beta testing" of this first distribution will lead to a better quality product when the data are released to the rest of the science community in late 1995.

The NEW data include climate, hydrographic, nutrient, and phytoplankton data from the North East Water area.

As part of NSIDC's ARCSS/OAII data support, an Arctic-wide solar radiation data set is being collected. With the generous cooperation of Tom Ross, NOAA/NCDC, an Arctic subset of the US solar radiation data on the NCDC "SAMSON" CD-ROM will be included in the ARCSS/OAII product.

The Arctic data will be made available to ARCSS/OAII and SHEBA investigators. Distribution to others outside ARCSS may be limited to certain data sets; negotiations are still in progress regarding possible distribution restrictions for data obtained from some contributors.

Some of the data are available now via ftp. Please contact NSIDC User Services for current information.

The NSF Office of Polar Programs (OPP) has supplemented the NSIDC ARCSS Data Coordination Center grant to include support for the rescue and preservation of certain data sets and related infrastructure in the former Soviet Union that are in immediate risk. Data management by NSIDC and the co- located WDC-A for Glaciology will be carried out within the framework of the International Permafrost Association Working Group on Permafrost Data and the NSIDC ARCSS data project. The rationale for focusing on permafrost data is the need for input to and validation of global climate change scenarios, and development of protection strategies for terrain underlain by permafrost.

Data thus rescued and archived will be made available to the research community as part of the ARCSS Data Coordination Center data distribution activities on CD-ROM, PC diskette, and via ftp.

MEETINGS

The AVHRR Polar Algorithm Workshop, hosted by NSIDC in Boulder on July 14 and 15, was very successful, with about 30 attendees and 14 presentations on the current status of several polar geophysical product algorithms that use AVHRR image data for input. In particular, the meeting focused on those algorithms that are at an appropriate stage of development for incorporation into a near-real-time processing routine using the Polar 1-km AVHRR Data Set, archived by NSIDC since August of 1993.

The primary processing-related challenges discussed during the meeting were geolocation and cloud detection. Results of the discussions suggest that it should be possible to generate images geolocated to within 1 or 2 km from the broadcast satellite ephemeris data, if a correction for onboard clock drift is included. This was demonstrated in talks by Dan Baldwin and Dr. Chuck Fowler of the Colorado Center for Astrodynamical Research of the University of Colorado. Recent success with cloud detection and classifying using Landsat TM and AVHRR data was presented by Dr. Ron Welch of the South Dakota School of Mining and Technology. A plan to further explore the use of Dr. Welch's software as part of a processing scheme for the Polar 1-km AVHRR Data Set was discussed. NSIDC is assembling a suite of polar AVHRR scenes for testing the software.

Presentations of the recent status of sea-ice motion and ice surface temperature algorithms were given by Dr. Chuck Fowler, Dr. Axel Schweiger, University of Washington, and Dr. Jeff Key, University of Colorado. Sea ice motion over the course of an entire year has now been mapped for the Beaufort Sea, and an analysis of the relative effectiveness of 4-km resolution GAC data and 1-km LAC and HRPT data was discussed. Dr. Key presented a processing scheme for a more complete derivation of the radiative transfer parameters for the poles using AVHRR (including the TOVS portion of the data stream, which is included in the NSIDC archive for some of the scenes) and some in situ data. Dr. Ron Lindsay, University of Washington, presented recent work on calculating polar albedo from AVHRR for the northern hemisphere ice pack and applying the results to lead fraction estimates.

Dr. Dorothy Hall, from NASA's Goddard Space Flight Center, presented a current evaluation of the status of snow-cover mapping algorithms using the MODIS Airborne Simulator (MAS) and Landsat TM. This algorithm is applicable to AVHRR data once the improved AVHRR/3 sensor is flown on the NOAA-K satellite (scheduled for early 1996). AVHRR/3 will include an additional band useful for snow/cloud discrimination at ~1.6 micrometers. Two representatives from the Alaska SAR Facility, Dr. Ron Wade and Ms. Joanne Groves, discussed algorithms that combine SAR and AVHRR data in Intensity-Hue-Saturation image transformations, in which the higher-resolution SAR imagery becomes the intensity component, and various band combinations of the AVHRR sensor are used to control hue. This technique was applied to yield sea-ice images color coded for surface temperature over a portion of the Beaufort Sea. Dr. Robert Bindschadler, also from Goddard, presented an overview of AVHRR applications to ice sheets, highlighting albedo measurement, ice dynamics feature mapping, ice surface temperature, and photoclimometry. Dr. Bindschadler pointed out that significant ice dynamics features, such as an ice-stream-like feature recently discovered in northeastern Greenland, lurk within the polar ice sheets, and are particularly well-resolved by high-radiometric-resolution, broad-scale sensors like AVHRR. Dr. Ted Scambos of the National Snow and Ice Data Center presented recent research on developing a data cumulating algorithm for application to mapping of polar land ice surfaces. This algorithm seeks to improve the spatial and radiometric resolution of AVHRR data by combining several scenes of the same area into a composite scene. An example image, cumulated from 6 separate AVHRR scenes, was shown of the same north eastern Greenland ice feature as mentioned in Dr. Bindschadler's talk.

The second day of the Workshop was devoted to a discussion on how to proceed to implement the algorithms discussed in the previous day into a processing scheme for the Polar 1-km AVHRR Data Set. The consensus was that priority should be given to the cloud detection/clearing algorithm, sea-ice motion, and ice surface temperature, with sea-ice motion as the top priority because it does not depend heavily on cloud detection, since the vector field generated over a cloudy area is noisy and can be screened out. A proposal is planned to the NASA Pathfinder project to develop an AVHRR Polar Geophysical Product processing scheme during 1995 and beyond.

NSIDC would like to thank all the participants in the workshop, and hopes to continue to support this community in the future. A more extensive report on the workshop is available upon request from Dr. Ted Scambos at Internet: teds@icehouse.colorado.edu or (303) 492-1113 or fax (303) 492-2468.

NEWS FROM OTHER CENTERS

The upcoming Earth Observing System (EOS) has a potential to build a uniform database covering most glaciers of the world and to monitor changes in glaciers on a periodic basis. The EOS "AM Platform," scheduled for a 5-year mission with a launch in 1998, will carry ASTER (the Advanced Spaceborne Thermal Emission and Reflection radiometer), a three-part instrument being built by Japan. The spacecraft will be in a high-inclination (9800), Sun-synchronous orbit (10:30 AM equatorial crossings) that will repeat ground tracks every 16 days. ASTER is a high-resolution, multi-spectral, pointable, stereo imaging system that can observe all of the Earth's surface at latitudes less than 85 degrees. ASTER's three subsystems include capabilities to image across a 60-km swath in three visible and near- infrared channels (VNIR), six shortwave infrared channels (SWIR), and five thermal infrared channels (TIR), with pixel resolutions of, respectively, 15 m, 30 m, and 90 m.

One of us (HK) has been a member of the ASTER science team since the inception of the project and has worked to ensure that ASTER's capabilities and mission plan remain well suited to the task of glacier monitoring. We seek the input of the broader glaciological community to further ensure that the pertinent capabilities of ASTER are utilized to the fullest extent possible. The EOS policy is that copies of the digital data products will be available to anyone at the incremental cost of copying and delivering the data.

As the project is presently being developed, ASTER VNIR band 3 (0.8 æm) images of most of the world's glaciers would be acquired annually to support such goals as monitoring surface velocities of large glaciers containing trackable features and monitoring the areal extent of exposed ice where possible. This project should result in a uniform, global database at 15 m resolution. The system may allow measurements of changes in the positions of high-contrast glacial features, such as crevasses, to about 5 m precision using sub-pixel registration relative to immobile ground points. In areas of dirty alpine glaciers, VNIR data may be supplemented with SWIR data to assist in the discrimination of snow, ice, dirty ice, and rock/vegetation. The present plan is to acquire and process a complete stereo (25-m vertical resolution) image set of the world's glaciers for the first year and a complete monoscopic set in the following years, except for additional stereo and more frequent imaging of selected glaciers as needed. Multiple cover age and the use of regional weather records, climate models, and short- term weather forecasts in scheduling observations may help obtain nearly complete coverage under cloud-free conditions. This planned survey will build on current and previous projects, including 20 years of space-based observations of glaciers, such as observations by Landsat, SPOT, ERS, and, in the future, Radarsat.

A broad collaborative effort could potentially accomplish:

a periodic survey of the world's glaciers resulting in a uniform image data set;

monitoring of special events, such as glacier surges;

production of derivative maps giving areal extent of exposed ice and snow fields;

production of a periodic inventory of the world's glaciers, including a compilation of important scalar parameters, such as mean surface speed, length, width, area, transient snow line elevation, and temporal changes in these parameters.

We welcome any suggestions pertaining to the use of ASTER's capabilities for glacier monitoring. We are especially concerned about the development of:

glacier observation plans that will take best advantage of ASTER's capabilities;

a GIS system that will provide maximum versatility and compatibility with other users;

the best available software for co-registration, autocorrelation, and discrimination;

a GIS database of glacier locations;

a GIS database of regional weather patterns (especially cloud cover).

Any pertinent climate data, glacier maps at scales of 1:100,000 to 1,2,000,000, or ideas on how you think we should proceed with our planning and software development would be helpful and very much appreciated.

At present, we hope to coordinate, image acquisition for glacier areas and the Level 1 processing (radiometric and geometric calibration) of these data. Image analysis for changes is foreseen as a large task, and we hope that many institutions will become involved and be responsible for regions for which they have expertise.

Jeff Kargel will be the coordinator at USGS (Flagstaff), however, feel free to contact any of us directly. We would be pleased to send you additional information on ASTER if you would like. We look forward to hearing from you, and we extend our gratitude to those of you who have responded to our earlier outreach efforts. Telephone numbers, fax extensions, and e-mail addresses are listed as follows: